1. Field of the Invention
The present invention relates to light emitting diodes (LEDs) and to methods of fabricating LEDs. More particularly, the invention relates to an LED device having enhanced sideways light emission and a method of making such an LED. The invention also relates to use of LEDs.
2. Background Information
An LED is a special type of semiconductor diode made of direct bandgap semiconductor material. When a voltage is applied to the LED terminals electrons and holes flow into the p-n junction and when an electron meets a hole it falls into a lower energy level which releases a photon, the fundamental element of light.
FIGS. 1 and 2 schematically illustrate known top-emitting 100 and flip-chip 102 LEDs. The LEDs have a similar structure comprising a layer of p-type semiconductor material 102, a layer of n-type semiconductor material 103 and a light generating region or p-n junction 104 formed on a substantially transparent substrate of a material 105 such as Sapphire. Terminals 106, 107 are connected to the p-type and n-type semiconductor materials 102, 103 for supplying power to the LED. A small part of the p-type material 102 and p-n junction 104 are removed by etching to expose the n-type material 103 for connection of the n-terminal 107. The LED structure is mounted to a supporting member 109.
When a voltage is applied to the terminals 106, 107 light is emitted from the p-n junction 104 in all directions. Maximum light emission is in a direction perpendicular to the p-n junction 104, which includes a direction towards the supporting member 109. Several techniques are available to recover this non-productive light emitted towards the supporting member 109 including adding a reflective surface to the supporting member 109 or using a reflective dish for the supporting member 109.
Additionally in certain applications, for example in backlight illumination systems for liquid crystal display panels, it may be desirable to have a LED's light emission pattern spread in a sideways direction. Hitherto this has been achieved by complicated optical designs.
These and other conventional solutions to deficiencies with prior LEDs may make LED fabrication more complicated and the LED packaging unnecessarily bulky. Accordingly, is an object of the present invention to provide a LED device which overcomes at least ameliorates some of the deficiencies exhibited by prior LEDs.